Damper for crossbar switch select finger



April 25, 1967 c, VAZQUEZ L 3,316,512

DAMPER FOR CROSSBAR SWITCH SELECT FINGER Filed March 4, 1964 2 Sheets-Sheet 1 United States Patent Ofiice 3,316,512. Patented Apr. 25, 1967 ware Filed Mar. 4, 1964, Ser. No. 349,293 Claims priority, application France, Mar. 6, 1963, 926,981, Patent 1,361,935 9 Claims. (Cl. 335-112) The present invention relates in general to crossbar switches and more particularly to an arrangement for damping the oscillations of the select fingers mounted on the select bars of the crossbar switches.

Modern telephone systems utilize crossbar switches in which the selection of a crosspoint is accomplished by the operation of a select bar the function of which is to move each of the select fingers which it carries into a predetermined position beneath associated sets of contact springs. Thereafter, a connect bar or hold bar" is operated which forces one of the selecting fingers into frictional engagement with the actuating element of selected contact set and causes the operation of the selected contact set.

In the well-known type crossbar switches, the noted select fingers are formed from a relatively thin wire having a certain flexibility. One of the extremities of said wire is wound in a helical manner with the free end of the helix rigidly secured to the select bar. Some finger mounting arrangements are known in which the coils of the noted helix are threaded on a tab which is clamped onto the select, bar.

When a connection is completely effected, the select bar is released but the select finger associated with the last-operated contact set is locked in position and flexes to permit the select bar to return to normal. When the connection is released by the restoration of the connect bar, the select finger returns to its normal untlexed position on the select bar.

The select finger, when released from either of its two operated positions or when it is displaced during an operation of the select bar, has a tendency to vibrate. These vibrations may be reduced, both in amplitude and duration, by adding damping means so that the residual vibrations remain within acceptable limits as determined by the operating speeds of the crossbar switches utilized.

These known damping means usually consist of a simple metallic piece loosely held around the slender portion of the select finger. The shocks of the slender portion of the finger against the metallic piece cause most of the energy usually dissipated into vibrations to be absorbed. However, some oscillations of a high amplitude subsist, but since the duration of said vibrations is very reduced, the select finger is returned to rest in its initial condition before the next operation of the connect bar.

With the introduction of electronics in switching systems, maximal operating speed of the crossbar multiswitches is required and the known damping means have been unsatisfactory, since the vibration amplitude of the damped select fingers was still large and resulted in improper connections or failure of connections.

An object of the invention is to provide vibration damping means for select fingers which comprises a suitable elastic material arranged to securely encompass or loosely encompass the free part of the select finger, or to encompass the helix portion of the selecting finger to obtain a damping function which aids the prior-art dampers.

Another object of the invention is to provide a hollow section in the elastic damping element to engage the noted helix and to also provide an .aperture permitting either loose or tight passage of the spire portion of the finger therethrough.

A related feature is concerned with holding the elastic damping element on the finger mounting by forming the diameter of the hollow section smaller than the diameter of the finger support tab.

Another object of the invention is to terminate the hollow portion in a conic shape without any spire aperture so as to guide the extremity of said select finger through the damping element by the application of a force causing a puncturing of the damper.

According to another embodiment, the damping element is provided with a pre-formed channel which may be varied in length to vary the damping effect and to improve the guiding of the select finger during the positioning of the damping element on the select finger.

According to a still further embodiment, another feature of the invention relates to forming the damping element from an elastic material which vulcanizes at room temperature in order that the finger spires become embedded partially or fully in the self-vu-lcanizing material.

Various other objects and features will be disclosed from the following description which is given by way of non-limited example and with reference to the accompanying drawings which represent:

FIG. 1 shows a partial perspective view of a crossbar switch;

FIG. 2 shows an enlarged view of a selecting finger mounted on its support;

FIG. 3 shows the select finger of FIG. 2 having the select finger damper positioned thereon;

FIGS. 4 to 10 show cross-sectional views of the different embodiments of the select finger dampers.

FIG. 1 shows a portion of a crossbar switch, the operating principle of which is well-known and thereby will not be described in detail in the present description. In this switch, bars 1 are the usual select bars and bars 2 are the usual connect bars. Clamps 3 are mounted on bars 1 and are provided for securing the select fingers 4 to the bars 1. This figure also shows that the clamps mounted on the upper bar 1 may receive the inventive dampers 5 which are designed to attenuate the oscillations of select fingers 4 when they come back to their initial position. It should be noted that the clamps associated with the lower bar 1 have been represented without their dampers.

FIGS. 2 and 3 represent, on a large scale, the select FIGS. 4 to 10 represent various types and shapes of.

dampers according to the present invention. In all of these embodiments the clamps 3, or the clamp tabs or the slender portion of the select finger are surround with a plastic material which is capable of damping the oscillations of the select finger caused by the return of the select finger to its initial position.

In FIGS. 4, 5 and 6, dampers are shown which securely grip both the clamp tabs and slender portion of the select finger.

The damper of FIG. 4 comprises a cellular plastic material in the form of a parallelepiped containing a blind hole or recess 6, the diameter of which is smaller than that of the clamp tabs of the select finger. This recess is terminated in a cone shaped section which guides the selecting finger extremity when the damper is punctured during assembly to bring it to the position indicated in FIG. 3.

FIG. 5 represents a damper which differs from that shown in FIG. 4 by terminating the end of the damper to conform to a frustum of a cone.

In FIG. 6, the damper consists of a non-cellular plastic material. Since this material is less flexible than that described f-or FIGS. 4 and 5, the recess 6 has a diameter larger than that shown in FIGS. 4 and 5, but still smaller than that of the clamp tabs of the select finger. Also, the diiference in rigidity is balanced by diminishing the thickness 7 of the sides of recess 6. Thus, the damping result is approximately the same as that obtained with a cellular material. However, a guide hole 8 is provided which reduces the length of the material which must be penetrated by the end of the select finger during assembly. The finger is then gripped by the pierced part of the damper.

FIGS. 7 and 8 disclose dampers in which the select finger is gripped.

In FIG. 7, damper 5 includes a recess 6 which is terminated by a cone for the hereinbefore described guiding purposes. The diameter of recess 6 is longer than that of the helix of the selecting finger so that said helix is not strained by the damper, since the finger alone is gripped. However, an aperture 9 has been provided for entry into recess 6. The diameter of aperture 9 is smaller than that of the helices of the selecting finger and its length depends on the length of the tab clamp 3. The damper is then held in position by the sides of aperture 9 gripping the clamp tab.

The damper of FIG. 8 has the same characteristics as that of FIG. 7 except that the material chosen has a hardness higher than that of a cellular material. A- channel 8 has been provided in this damper which reduces the length of material to 'be pierced by the end of the selecting finger. In this figure, the select finger pin is gripped by the material which was pierced.

FIG. 9 shows a damper in which the diameter of recess 6 is smaller than that of the helices of the select finger. The thickness 7 of the sides of recess 6 is calculated in terms of the damping effect to be realized and the rigidity of the material used. A channel 10 enables the end of the selecting finger to pass freely through the damper. The diameter of channel 10 may vary according to the play chosen to be given to the select finger to increase or decrease the vibration damping. i

FIG. 10 shows an embodiment in which neither the helices nor the finger are gripped by the damper. T 0 this end, the diameter of recess 6 is greater than that of the helices of the selecting finger and aperture 10 has a diameter greater than the diameter of the select finger. The aperture 9, as previously described, holds the damper by clamping it on the tab of the clamp 3 of the select finger 4. However, the finger rests against the side of channel 10 so that the damping of the oscillations of the select finger depends on the diameter of aperture 10.

It is to be understood that the damper can consist of a plastic material which vulcanizes in the ambient air and thus may be used to imbed the helices of the selecting fingers. This material may be the result of the blending of two plastic components with air acting as a catalyst. In such an arrangement, the finger is free in its movements but the helices have lost much of their elasticity and consequently, diminish the vibration of the pin.

It is clear that the previous descriptions have only been given by way of non-limitative example and that numerous alternatives may be considered Without departing from the scope of the invention.

We claim:

. 1. In a crossbar switch, a select bar having a normal position and an ofi-n-ormal position, a resilient select finger and means for securing it to said bar for movement with said bar between said normal position and said off-normal position, elastic vibration damping means encircling said select finger near its junction with said select bar for dam-ping the vibration of said resilient select finger, said means for securing including select bar tab meanson said bar and tab gripping means on said-finger, and said vibration damping means encircling said tab gripping means and said finger.

2. A crossbar switch as set forth in claim 1 wherein said damping means tightly encircles said select finger and said tab gripping means.

3. A crossbar switch as set forth in claim 1 wherein said damping means tightly encircles said select finger and loosely encircles said tab gripping means.

4. A crossbar switch as set forth in claim 1 wherein said damping means tightly encircles said select finger and said tab means and loosely encircles said tab gripping means.

5. A crossbar switch as set forth in claim 1 wherein said damping means loosely encircles said tab clamping means and said finger and tightly encircles said tab means.

6. A crossbar switch as set forth in claim 1 wherein said damping means comprises plastic material embedding said select finger, said tab clamping means and said tab means.

7. Crossbar select finger damping means as set forth in claim 1 comprising a plastic material having a recess therein "for receiving said tab clamping means and having an extrusion characteristic permitting piercing of said material by said finger.

8. Crossbar select finger damping means as set forth in claim 7 wherein said recess comprises a configuration for guiding the select finger to pierce said damping means in a direction co-axial with said recess.

'9. Crossbar select finger damping means as set forth in claim 7 wherein said damping means includes a selectfinger aperture coaxial with said recess for permitting the free passage of the select finger through said recess and said aperture to position the said recess in receiving relation with said tab clamping means.

No references cited.

BERNARD A. GILHEANY, Primary Examiner.

R. N. ENVALL, JR., Assistant Examiner. 

1. IN A CROSSBAR SWITCH, A SELECT BAR HAVING A NORMAL POSITION AND AN OFF-NORMAL POSITION, A RESILIENT SELECT FINGER AND MEANS FOR SECURING IT TO SAID BAR FOR MOVEMENT WITH SAID BAR BETWEEN SAID NORMAL POSITION AND SAID OFF-NORMAL POSITION, ELASTIC VIBRATION DAMPING MEANS ENCIRCLING SAID SELECT FINGER NEAR ITS JUNCTION WITH SAID SELECT BAR FOR DAMPING THE VIBRATION OF SAID RESILIENT SELECT FINGER, SAID MEANS 